This invention relates to high strength reconstituted collagen fibers which are particularly well suited as grafts for orthopaedic, dermal, cardiovascular, and dental implants, prosthesis and other applications particularly in human subjects.
Collagen fibres are the structural elements that give shape to mammalian tissues as well as acting as the scaffold over which cells migrate and deposit new connective tissue. Types I, II and III collagen fibres in the form of cross-linked networks prevent over-expansion of the aorta and heart, limit shear deformation of cartilage and biaxial tensile stretching of skin and transmit tensile loads in tendons. Type I collagen fibers make up the connective tissue in various body parts of mammals like in tendons, skin, bone and fascia. The location and tissue source of different collagens are explained in Reference No. 82 which is incorporated herein by reference.
In the description which follows reference is made to publications identified by numerals in parenthesis, which are more fully cited towards the end of the description and which publications are all included herein by references. Also other publications are listed which are of background interest.
Currently no synthetic material is available to satisfactorily replace the function of normal tendon or ligament indefinitely. No biodegradable or polymeric synthetic tendon or ligament is available which provides mechanical properties equivalent to an autograft or which induces repair by tissue ingrowth. Such a material would be valuable in tendon or ligament reconstruction as a substitute for autograft material. Synthetic polymers developed for tendon or ligament replacement utilize permanent fiber bundles or monofilaments designed to directly bear load for the life of the implant. These implants can fail as a result of fatigue and require surgical removal of graft remnants.
Implants which encourage neotendon formation have also been developed. However, none have proven to stimulate collagenous ingrowth with mechanical characteristics resembling normal tendon.
Several approaches have been tested to replace the function of tendons and ligaments damaged as a result of athletic injury. Replacement of tendon and ligament has been achieved using biodegradable and non-biodegradable synthetic polymers and biological tissues from the knee. But these also have short comings as yet unsolved.
Non-porous polymeric implants have a limited fatigue life and ultimately fail when used to replace the function of a ligament such as the anterior cruciate. Implanted tows of polymeric and carbon fibers result in the controlled formation of a "neo-tendon" through the deposition of aligned collagen. Biological structures such as glutaraldehyde-fixed bovine tendon and autogenous tendons and ligaments elongate after surgical implantation and eventually do not support loads in the knee.
These methods all require a lengthy rehabilitation period. These prior art techniques are well described in background literature in references 9, 10, 11, 14, 15 and 17.
Autologous tendon transfers now provide the only long term solution to traumatic tendon or ligament loss. This is reported in literature references 1, 2, 3 and 9. There are however, serious drawbacks to the use of autogenous tissues. Autograft materials or autologous transfers are not readily available; also they cause loss of normal functioning of the structure and a slow rate of incorporation and maturation of repair tissue. Further, the extensive use of autologous tissue is potentially disabling and disfiguring to the individual.
This description shows how unsatisfactory autologous materials are in repair or replacement of tendons, ligaments, etc.
From the description of the prior art it is evident that a serious and urgent need exists for high strength fibrous materials suitable for use as a graft that is long lasting and has biocompatibility with a host, which graft has the desired properties.
The graft of the invention overcome many of the prior art difficulties and problems and have a combination of advantageous properties non-existance in the prior art. The collagenous graft used of the invention can be manufactured without sacrifice of the host's tissue. The graft of the invention quickly incorporates the repair tissue which is a needed characteristic in the design of biomaterials that enhance the deposition of repair tissue in skin, tendon and the cardiovascular system. Although high-strength oriented and unoriented collagenous materials are reported in the literature (22) no report is known of collagen fibers of small diameter that can be processed into woven and non-woven textile prostheses which have the necessary properties that simulate or exceed those of the natural body part.
In this description of the invention, the following terms have the following meaning:
"Autograft" means transferring a tissue or organ by grafting into a new position in the body of the same individual.
"Implant" means a graft which is woven into and secured in the surrounding tissue.
"Graft" means anything inserted into something else, or contacted upon something else so as to become an integral or associated part of the latter and it includes materials and substances which are either added to an already intact structure or serve as a replacement substitute or repair to a damaged or incomplete structure. Thus a "graft" is intended to be given the broadest possible meaning and encompasses a prothesis, implant or any body part substitute for any mammal (animal or human).
The invention provides collagen grafts for numerous applications particularly where high tensile strength and biocompatability are essential. It is evident that both of these properties are essential for grafts. If tensile strength is not high enough or of limited duration, there is the real risk that the graft would rupture (or weaken). Thus, physical integrity is essential. Biocompatability is also necessary otherwise rejection of the graft could occur. The invention also provides collagen proteoglycan fibrous grafts which have even greater tensile strength than the non-proteoglycan grafts of the invention. These are especially well suited for specialized applications where such property is particularly important. The invention further provides a method for making improved collagen proteoglycan fibers for use in such grafts.
The invention provides further implants in which the collagen grafts are woven and secured into the surrounding tissue. The surrounding tissue then invades the graft material. The graft is revascularized and eventually replaced by the host's tissues.
The invention further provides for grafts with physical properties that can be manipulated or processed into a variety of shapes, thicknesses, stiffnesses in woven or non-woven forms.
Other embodiments provided by the invention will become apparent from the description which follows.
The invention contributes to fulfilling a serious need in the medical, bio-medical, cosmetic, body-repair, body reconstruction and related arts.